VIVA – Anatomy – LARYNX Flashcards
Draw the muscles of the larynx
What is the innervation of the larynx?
Motor
All intrinsic muscles except for cricothyroid supplied by RLN
Cricothyroid supplied by external laryngeal branch of superior laryngeal nerve
Sensory innervation
Also mediated by vagus nerve
Supraglottis supplied by internal laryngeal branch of superior laryngeal nerve
Glottis & subglottis supplied by RLN
Autonomic Innervation
SNS via Superior and inferior laryngeal arteries from the middle and inferior cervical ganglia
What is the embryology of the larynx?
- Begins as the laryngotracheal groove at the ventral aspect of the foregut (week 4)
- this groove deepens into the laryngotracheal diverticulum develops ventral to the pharynx
- ventral endoderm → larynx and trachea
- caudal endoderm → bronchi and lungs
- epithelium from endoderm, cartilage/muscular/connective tissue from splanchic mesoderm
- initially in open communication with foregut à longitudinal tracheo-oesophageal folds develop and begin to separated laryngotracheal diverticulum from the foregut
- these fuse to become the tracheooesophageal septum which divides the foregut into a ventral laryngotracheal tube and a dorsal oesophagus
- Larynx develops from the 4th and 6th branchial arches with the laryngotracheal opening lying between these 2 arches (week 5-6)
- Growth of 3 tissue masses;
- hypobranchial eminence
- Mesodermal structure
- from the 3rd and 4th arches
- Develops into the epiglottis and some base of tongue
- 2 arytenoid masses (paired ventral ends of 4th arch)
- these two lateral swellings migrate cranially and medially to oppose each other and, together with the epiglottic swelling, surround a T-shaped laryngeal aditus
- hypobranchial eminence
- 3 masses grow toward the midline forming a T shaped aditus and obliterate the laryngeal lumen at weeks 5-7 à laryngeal lumen becomes occluded at 8 weeks of gestation due to epithelial proliferation
- Subsequent vacuolization and recanalization produce laryngeal ventricles
- Re-canalization by week 10. Failure to do so → atresia, stenosis, webs.
- Interarytenoid notch separates 2 arytenoid masses. If this does not obliterate a posterior laryngeal cleft can result
- formation of the VC and FVC is related to the condensation of mesenchyme and the outpouching of the laryngeal sinus or ventricle
- two vocal folds separate during the 3rd gestational month, and failure of this recanalization process results in congenital atresia of the larynx
- laryngeal cartilages develop from the BAs, with the more cranial cartilages possibly arising from the 4th arch and the more caudal ones from the 6th
- thyroid cartilage develops from the 4th arch as two lateral plates that fuse in the midline
- this process is almost completed by the 9th gestational week
- cricoid cartilage appears to begin as two cartilaginous centres of the 6th arch
- first, the centres grow and unite in the ventral midline; then, by the 7th gestational week, they fuse dorsally
- rostral advancement of the tracheoesophageal septum results in the fusion of the dorsal cricoid lamina
- failure of advancement of this septum results in a fistula
- at first, the cricoid lumen is slit-like in shape, but eventually the ventral and lateral walls of the cricoid cartilage condense and there is progressive enlargement of the lumen
- failure of this condensation process results in congenital subglottic stenosis
- arytenoid cartilages develop from the arytenoid swellings, most likely derivatives of the 6th arch but possibly arising from the 4th arch
- they are initially fused to the cricoid cartilage, but they eventually separate from it and form the cricoarytenoid joints
- intrinsic laryngeal muscles develop from the mesoderm of the 4th through 6th arches
What are the differences between the infant and adult larynx?
- Higher: this enables simultaneous feeding and breathing (normal by age 6)
- cricoid at C4 in infant, C6 in adult
- Epiglottis rises superiorly and lies against nasopharyngeal surface of soft palate à obligate nasal breather for 4-6/12 à interlocks while feeding
- Funnel-shaped
- Cricoid is the narrowest portion – until 8 y.o (cf glottic aperture)
- 6/12 – 6-7mm
- 10 y – 8-11mm
- adult female – 13-18mm
- adult male – 15-22mm
- Is slightly anterior to the horizontal axis (tilted) post tilt of cricod lamina produces funnel shape with oval inlet and circular outlet cf adult inlet = outlet
- Rigid nature of cricoid – most narrow area also most unyielding to compressive forces
- Lack of substantial submucous layer – less protection against shearing and compression
- infant larynx is 1/3 of the size of an adult larynx
- proportionately larger in the infant compared with the rest of the tracheobronchial tree
- vocal process
- takes up ½ the length of the cord in the infant compared with ¼ in adult
- VCs 6-8mm (14-23 in adults)
- compliance
- infant airway more pliable and soft tissues less adherent to underlying structures. More susceptible to collapse and oedema formation.
- epiglottis
- omega shaped. Sits higher, resting on the posterior nasopharyngeal wall. Can collapse with deep inspiration.
- aryepiglottic fold disproportionately large as cuneiform cartilages relatively much larger and may obscure arytenoids
- laryngeal saccule is variable in size – may be seen on xr
- arytenoid adult size at birth
What is the angle of the thyroid cartilage in the male & female?
Male- 90
Female- 120
Where are the Corniculate cartilages?
Articulates with apex of each arytenoid
Where are the Cuneiform cartilages?
Lie within aryepiglottic folds and are unimportant
What are the movements of the arytenoid cartilages?
Lax capsule of cricoarytenoid joint allows rotary and lateral gliding movement
What shape does moving arytenoids produce in the glottis?
Move laterally and downward along sloping shoulders of cricoid to open glottis in a “V”
Rotation alone opens glottis as a Diamond
Because of the geometry of joint surfaces, which are slightly saddle-shaped, the lateral movement is accompanied by a small amount of rotation.
In man there is a greater range of gliding than of rotary movement, and the open human glottis resembles a V and not a diamond
What are the attachments of the quadrangular membrane?
Anterior border attaches to lower half epiglottis
Posterior border attached to anterolateral surface arytenoid
Lower Border is free forming Vestibular Ligament à False cord
Upper border is aryepiglottic fold
What is the histology of the glottis?
5 layers (Hirano)
(i) Squamous epithelium - non-keratinizing, stratified squamous
(ii) Superficial layers of lamina propria
- loose connective tissue fibers and matrix
- Reinke’s space = potential space
(iii) Intermediate layer of lamina propria
- more densely arranged elastic fibers and collagenous
- parallel to the free margin of the vocal cord
- forms the bulk of the macula flava
(iv) Deep layer of lamina propria
- closely packed collagen fibers
- forms the vocal ligament with the intermediate LP
- continuous with the anterior commissure tendon
(v) Vocalis muscle
- the main body of the vocal cord
- most medial fibers of thyroarytenoid muscle
What layer will you dissect in vocal fold for Benign lesions?
- principles are to preserve normal structure and function
- microflap approach involving incision of epithelium near lesion and away from free edge of vocal cord
- dissection in the avascular plane of the superficial LP using blunt dissection probes
- intact epithelial flap is then replaced
What layer will you dissect in vocal fold for Malignant lesions?
Depends on depth of invasion
What is you management of laryngeal dysplasia?
Laser/cold steel excision with follow up MLB 6/52 post
Overall risk of invasive Ca 16.7%
Could consider autoflurescence to watch
Discussion in H&N clinic if ongoing dysplasia/difficult access/CIS
What is your technique for vocal cord stripping?
Generally no longer done – poor voice and scarring post
Draw where you would inject for injection thyroplasty
Injection of material (abdominal wall fat, fascia, collagen, gelfoam, calcium hydroxyapatite, hyaluronic acid) into paraglottic space deep to thyroarytenoid muscle, lat to vocalis
What are the boundaries of the Pre epiglottic space?
Bounded by hyoid bone, hyoepiglottic ligament and valleculae superiorly, thyrohyoid membrane and thyroid cartilage anteriorly, & epiglottis (and thyroepiglottic ligament) posteriorly
Laterally it is continuous with the paraglottic spaces
What are the boundaries of the Paraglottic space?
- Borders
- Lateral - Inner perichondrium thyroid cartilage (anterolaterally) and cricothyroid membrane inferolaterally
- Medial – Conus Elasticus and Vocal Lig (inferomedially), Quadrangular Membrane and laryngeal ventricle
- Pyriform sinus mucosa is posterior-laterally
- Anterior inferior PGS can extend beyond the larynx beneath the inferior rim of the thyroid cartilage
- Contents
- Loose areolar tissue
- Elastic and adipose tissues
- Adipose tissue extends between the caudal fibres of the thyroarytenoid muscle
- In theory connects to pre-epiglottic space, but growth & invasion along this potential path unusual
- Coherent collagenous fibrous septum present in some people
